Project summary Meiosis is a specialized cell division characterized by a single round of DNA replication followed by two rounds of chromosome segregation, resulting in the formation of gametes. Cohesin is a chromosome-associated multiprotein ring that maintains sister chromatid cohesion, and which is essential for accurate chromosome/chromatid segregation. During meiosis, cohesin disassembly is particularly complicated by the requirement for sequential loss of cohesion along the chromosome arms at the first meiotic division (MI) and then at the centromere during the second meiotic division (MII). NIMA-like kinase 1 (NEK1) is a dual specific serine/threonine and tyrosine kinase that is highly expressed in germ cells. Loss of NEK1 in mice leads to retention of the cohesin subunit SMC3 on chromosome arms at MI and subsequent infertility. Cohesin removal is orchestrated in two steps, first by ?the prophase pathway?, followed by Separase-mediated cleavage of the cohesin ring. The prophase pathway is defined by the stoichiometry between the Wings-apart-like protein (WAPL) and Sororin, which compete for binding to PDS5B on the cohesin ring, but this pathway has not yet been described in meiosis. My preliminary data reveal exciting roles for NEK1 in the regulation of cohesin dynamics at MI, both directly at the level of the cohesin subunits, SMC3, RAD21L and REC8, and indirectly through phosphorylation the PDS5B-WAPL complex. Furthermore, my studies have shown that NEK1 action on the prophase pathway is mediated via Protein Phosphatase 1-gamma (PP1?), which is a phosphotarget of NEK1, and which binds and de-phoshphorylates WAPL. Moreover, my preliminary studies indicate that NEK1 also regulates a cascade of other NEK proteins to perform other roles in MI that are distinct from its activity on cohesion dynamics. Thus, I hypothesize that NEK1 acts as master regulator of events in meiosis, primarily playing a crucial role in the timing of cohesin removal at MI through its actions on critical components of the prophase pathway, but also in orchestrating the actions of other NEK kinases. My long term goal is to elucidate how NEK1 regulates cohesion removal at MI, but also to further characterize the role of NEK1 catalytic activity in orchestrating downstream events at both meiotic divisions. Three specific aims are proposed: (1) To elucidate the role of NEK1 in the phosphorylation of PP1?, (2) To assess the importance of WAPL phosphorylation on cohesion removal at MI and (3) To elucidate the function of NEK1 as a master regulator of the NEK family during meiosis. These experiments will provide a novel and exciting data that describes, for the first time, the the role of NEK1 in the regulation of cohesin removal during the prophase pathway in meiosis. The applicant, Dr. Brieo-Enrquez, is an MD, PhD with considerable experience in the field of gamete biology. The applicant has studied distinct process of gamete biology in humans and mice, with a goal to understanding the complex events that give rise to healthy gametes for sexual reproduction. The ultimate goal of the applicant is to establish a unique and state-of-the-art research program aimed at understanding how mammalian meiosis and gametogenesis is regulated and what events may be defective in humans, where the error rates associated with meiosis are exceptionally high. Thus, a career development plan has been established to provide Dr. Brieo-Enrquez with all the necessary tools to establish a robust research program in a stellar academic institution. In addition to the best scientific resources available, Dr. Brieo-Enrquez will benefit from a wide variety of workshops and seminars available at his host institution, Cornell University. Topics include job searches, preparing an application and preparing for an interview, negotiating a startup package, establishing a lab, and building an effective research team. In addition, there are courses devoted to improving teaching skills, writing grants, and dealing with conflict in the work place, to mention just a few. Dr. Brieo-Enrquez will also benefit from an outstanding mentoring team, led by his mentors, Dr. Paula Cohen and Dr. Mark Roberson, both highly regarded in the field of Reproductive Biology, and both having much experience in mentoring successful postdoctoral fellows. Supporting this mentoring team is an outstanding advisory committee consisting of experts in the field of kinase biology (Dr. Marcus Smolka), cohesins (Dr. Michael Goldberg), mouse transgenesis and reproduction (Dr. John Schimenti). The applicant will meet frequently with his mentors and advisory team, both informally and formally. Moreover, the mentors and advisory committee have committed to assisting Dr. Brieo-Enrquez as he develops his research skills, and will help him to craft a strong faculty application, job seminar, and chalk talk. Lastly, Dr. Cohen has committed to supporting Dr. Brieo-Enrquez financially through his research and to providing ongoing mentorship as he transitions to his newly independent position. In summary, Dr. Brieo-Enrquez has devised an exciting and novel proposal that seeks to define the role of the NIMA-like kinases in the meiotic cell divisions. In doing so, he will create a robust and novel niche for himself in the field of gamete biology. To assist him, he has assembled a world-class mentoring team and a strong development plan, all with a unified goal of promoting the successful transition to independence of this exciting young scientist